Fermented milk is a paste or liquid product obtained by fermenting milk, or milk or the like containing solid contents of nonfat milk at the same level or higher, with lactic acid bacteria or yeast, or a dried product thereof, and is broadly classified into two types. One is a pre-fermented type, while the other is a post-fermented type. The former is produced by packing into an individual container for distribution the fermented milk crushed after the completion of fermentation and cooling in a tank before packing into a container. The latter is produced by packing a mix of raw materials for fermented milk added with a predetermined amount of a starter (referred to as mix hereinafter) into an individual container for distribution such as a paper container, and subsequently fermenting the mix in a fermentation chamber until the lactic acid acidity reaches a predetermined level for solidification into a purine-like state, followed by cooling. The pre-fermentation is commonly used for producing fruit yogurt with fruit flesh, drinking yogurt and the like, while the post-fermentation is commonly used for producing yogurt of so-called hard-type and plain-type, and the like.
In any case of the fermentation types, a starter is added to a sterilized mix at a predetermined temperature, and fermentation is carried out until the acidity reaches a predetermined acidity at the fermentation process. Then, the resulting product is cooled for terminating fermentation, to prepare a final product. Because the fermentation temperature and fermentation time at this period not only influence the production efficiency of the product but also give significant influences on the flavor and quality, it is necessary to set the fermentation temperature and the fermentation time appropriately with taking those influences into account. For example, the fermentation temperature should be set lower in a case of intending to give mild flavor to the product.
Herein, the production efficiency and product quality may be problematic since the fermentation time required to reach a given acidity is significantly prolonged in comparison with a usual method, and additionally, the texture hardness is so low that the texture may degrade during distribution process, for example in a case of setting the fermentation temperature lower to give mild flavor to the product. Accordingly, it has been very difficult to obtain fermented milk having mild flavor and a texture with hardness not degrading during distribution process.
No direct method for improving such present situation has been reported yet. However, the following approaches have been carried out as applicable methods. The first approach includes a method with adjusting conditions in which the efficiency of fermentation process is improved to shorten fermentation time. It is considered that such approach enables fermentation at a fermentation temperature lower than a usual method, other than the achievement of the purpose of improving the production efficiency. The second approach includes a method with selecting lactic acid bacteria which produce substances giving mild flavor. A third approach includes a method with giving additives improving flavor to such a product to give necessary texture such as mildness, without any modification of fermentation process.
As examples of the first method for promoting fermentation, a method which includes adding a whey protein concentrate (JP-A-11-028056) and a method which includes adding butter milk (JP-A-09-201164) have been proposed.
However, in these previous examples, low-temperature fermentation was not assumed, and it was not investigated whether or not fermentation can be promoted at low temperature. As an example of the second method, a method which includes fermentation with a selected lactic acid bacterium for use, to make L-lactic acid occupy 85% or more of total lactic acid bacteria to give a fresh and mild flavor to the fermented milk has been proposed (JP-A-06-327401). As an example of the third method, a method which includes adding amino acids having a specific composition to the fermented milk for improving the flavor has been proposed (JP-A-10-327751).
Any of these methods involves the addition of some substance to fermented milk or the modification of the composition of the components thereof. Therefore, it is inevitable to design the product while taking account of the influences of additives and the like over product flavor, quality and the like. In other words, these methods can neither improve production efficiency while the product feature of the original product is maintained without using additives and the like, nor add “mild flavor” while the production efficiency and the product feature of the original product is maintained.